The invention relates to a wiper arm as generically.
Known windshield wipers have a wiper arm, which is made up of a driven fastening part, a joint part connected to it via a toggle joint, and a wiper rod rigidly adjoining the joint part. The windshield wiper also have a wiper blade, which has a support bracket system and a wiper strip retained thereby. The wiper blade is pivotably connected to the wiper arm in that a hooklike end of the wiper rod engages between two lateral cheeks of the support bracket system and includes a pivot pin. The joint thus formed guides the wiper blade with the wiper strip over the motor vehicle window; the joint part and the support bracket system make it possible for the wiper strip to adapt to a curvature of the motor vehicle window. A required contact pressure of the wiper strip on the vehicle window is attained with at least one tension spring, which braces the fastening part and the joint part, jointly with the wiper rod, via the toggle joint.
The shape of the individual components of the wiper arm is influenced by various demands and stresses; specifically, they should be as torsionally rigid, deflection-resistant, and narrow in the field of view as possible, so that the wiper blade can be guided without vibration and under control over the vehicle window yet present little hindrance to the field of view.
The fastening part transmits the drive moment from the drive axis to the wiper blade, via the joint part and the wiper rod. It also forms part of the toggle joint, by way of which the fastening part is braced with the joint part by the tension spring and pressed in the direction of the vehicle window. The greatest forces or moments arise in the fastening part, both parallel to the window and perpendicular to the window. Furthermore, deformations in the lower region of the windshield wiper have an especially strong effect over the entire length and can cause uneven wiping speeds as a result of a spring effect. The fastening part and the first portion of the joint part must therefore be embodied as especially deflection-resistant and torsion-resistant.
In a wiping motion, the second portion of the joint part moves partly, and the wiper rod moves completely, through the field of view of the driver, and as a result they must be made not only torsion- and deflection-resistant but also especially narrow, so that the impede the view as little as possible.
Furthermore, the wiper arm should be shaped in such a way that it is not listed away from the vehicle window by the relative wind.
Known wiper arms have a wide fastening part and a joint part that is made of sheet metal and that is still relatively wide in the region of the fastening part, that is, at the lower edge of the field of view, often with a U profile that is open toward the window. Because of its favorable resistance moment, it is especially torsion- and deflection-resistant in this region, and the tension spring can be received, concealed, in the U profile. In the direction toward the free end or toward the connection point with the wiper rod, the joint part tapers so that it is narrow in the field of view. Over the full length of the joint part, the profile has a constant material thickness, determined by the sheet metal used; this thickness is designed for the desired dimensional stability at the greatest material stress to be expected, which is substantially composed of bending and torsion stresses, specifically perpendicular and parallel to the vehicle window.
As a rule, the wiper rod is formed by a rod profile of constant material thickness, which is crimped to the joint part.
The material stresses in the wiper arm depend on various factors. On drive forces and contact pressure forces, on their engagement points, lever arms, and on resistance moments of the wiper arm. Since the shaping cannot be adapted solely to the courses of stress and to sagging, but instead still other aspects must be considered, such as creating a space for stowing the tension spring, effective wind engagement faces, and in particular a slender structure in the field of view, and so forth, great and variable material stresses occur at various points. Often, the material demands are greatest in the connection point of the wiper rod to the joint part and in the wiper rod itself, because of the small cross-sectional area and unfavorable resistance moments. The material thickness of the joint part is determined by the material stress at the connection point with the wiper rod, and the wiper rod is entirely formed of a thicker material.
Since the material thickness for the joint part and for the wiper rod must be designed for the greatest material stress, regions subject to less stress are made oversized. This means unnecessarily high consumption of material, high material costs, and high weight, and this is all the more true if the parts made of sheet metal are meant to be made from sheet-metal panels of constant thickness or integrally.
According to an embodiment of the invention, for the portions of the wiper arm formed of sheet metal, that is, the fastening part and in particular the joint part and the wiper rod, a variable number of material layers can be folded up onto one another in various regions, until the material thickness required for the particular cross section is attained. The material can be bent over a single time or multiple times by approximately 180xc2x0, or distant surface regions can be folded up in one or preferably multiple steps in order to brace one another.
The folded-up material layers act over all in the corresponding regions virtually like a material that is thicker throughout. Thus from a relatively thin sheet metal, different material thicknesses can be attained in different regions, and these thicknesses can be adapted exactly to different stresses that arise. Only in the regions subject to high material stresses are greater material thicknesses attained by the folding technique. Over all, a thinner sheet-metal thickness can be used for these parts. Furthermore, the faces resting on one another damp vibration and thus largely suppress jittering of the wiper strip on the vehicle window, or cause any jittering to fade again quickly.
The connection point of the wiper rod to the joint part is usually already located fairly far into the field of view and must therefore be made narrow, with a small cross-sectional area. Furthermore, often along with high material strains from the drive moment and strains from the tension spring occur from the fastening of the wiper rod to the joint part, and these are superimposed on the other material stresses. In one embodiment of the invention, it is proposed that the joint part be reinforced, in the region of the connection point with the wiper rod, by a plurality of material layers folded onto one another, thus compensating for the small cross-sectional area.
The proportion of the area that is multilayered can be varied with infinite graduation via the length of the portions, for instance by having one layer taper obliquely in the longitudinal direction. As a result, the portions can be adapted favorably to constant moment courses, or to courses of material stress.
In order not to limit the field of view, the joint part tapers greatly longitudinally from the drive axis to the wiper rod. As a result, the cross-sectional area decreases and the material stress increases. It is therefore proposed that with respect to the cross-sectional area, the portion having a plurality of material layers folded onto one another increase longitudinally. If the joint part has an advantageous U profile, this is attained in that beginning at the articulation point to the fastening part, lateral cheeks first and then adjoining them a top side of the U profile are embodied increasingly with two or more material layers.
In addition, it is also possible to achieve higher resistance in targeted individual regions, for instance those where forces attack them directly, by folding two or more material layers onto one another in these regions.
By the folding technique, low material costs are attained by thinner sheet-metal thicknesses, less trimming waste, and low weight. At low sheet-metal thicknesses, it is also possible to use more-economical, more weakly dimensioned cutting tools, so that a smaller interstice is needed between the forms to be cut out. As a rule of thumb, a spacing of three times the sheet-metal thickness should be maintained. Lesser sheet-metal thicknesses thus lead to less trimming waste.
Along with the described economies and favorable design options, transitions of attractive shape between different material thicknesses in an one-piece component can be created using the folding technique.
The sheet-metal parts known until now for the wiper arm are partly cut out side by side from a larger sheet-metal panel, so that upon further deformation they do not affect one another and still can be transported favorably. Especially with the tapering form of the joint part, when the sheet-metal parts are aligned identically, there is a large area of trimming waste in the narrower region. According to the invention, it is proposed that this area be utilized as fold faces. The sheet-metal parts are thus made from one-piece flat sheet-metal panels with contour faces and with fold faces adjoining the contour faces. The contour faces are used for the fundamental shaping of the sheet-metal part, and the fold faces are used for fastening regions and, to attain different material thicknesses. The material is better utilized; that is, trimming waste is largely avoided, and the material costs are thus reduced. If furthermore in the flat state of the sheet-metal part the fold faces are located in a rectangle defined by the contour faces, and if this rectangle is virtually entirely filled with the two faces, the material can be utilized even better, and trimming waste can be reduced still further. It is also possible for the fold faces to extend past the rectangle and to be supplemented with fold faces of adjoining identical or different components with an identical or different alignment.
In known wiper arms, the wiper rod is secured to the joint part on one end, for instance being crimped, welded, etc. In this end, in known wiper rods, a spring hanger is made in the form of a hole for a tension spring, with which the fastening part and the wiper rod are jointly braced with the joint part. The wiper rod extends past the region of fastening to the joint part in the direction of the fastening part, so that the tension spring can be made shorter and can be favorably disposed in the still-wider lower region of the joint part. In one feature of the invention, the spring hanger is formed onto the joint part. The wiper rod can be made shorter as a result, thus saving material, weight and expense. The spring hanger can be made in a single-walled contour of the joint part. According to the invention, however, the spring hanger is formed from fold faces onto the joint part, so that favorably a spring hanger that is concealed from the outside and is adapted exactly in terms of wall thickness to the stress can be attained without weakening the contour of the joint part by making recesses in it.
As already described above, the wiper rod is usually joined to the joint part by crimping. If the joint part, in the region of the connection point with the wiper rod, has a plurality of material layers and if at least the material layer that comes into contact with the wiper rod has one or more detent holes, then favorable snap connections that can be made releasable can be created between the joint part and the wiper rod. The complicated connection by crimping is dispensed with, and even already painted wiper rods and joint parts can be joined together. If the detent holes do not pass through all the material layers and are thus concealed from the outside, then no water or dirt can collect in them, and thus attractively shaped snap connections that are not vulnerable to corrosion or dirt can be created.
If the joint part, in the region of the connection point with the wiper rod, has a hollow profile, then the wiper rod can be secured especially securely in a torsion-and deflection-resistant way. The hollow profile can have detent holes on its top and bottom sides for the wiper rod.
In one feature of the invention, the joint part and wiper rod are made of a one-piece sheet-metal part. The wiper arm has fewer individual parts and can be made in an attractive shape without a transition between individual components. This also saves one assembly step in joining together the wiper rod and the joint part. Since the wiper rod is located directly in the field of view, it should be made especially narrow with a small cross section. To compensate for the small cross section and attain a sufficiently torsion- and deflection-resistant wiper rod, it is proposed that the wiper rod be formed of at least two material layers folded onto one another.
In relatively short wiper arms, for instance for rear-window wipers, the production material is utilized well despite the one-piece joint part and the wiper rod, without producing major quantities of trimming waste. With longer wiper arms, sheet steel is preferably used, so that for an acceptable material thickness, a sufficiently rigid construction can be achieved.
Before the sheet-metal parts are bent or bent over in production, recesses are made in the still-flat sheet-metal panels; after the bending operation, these recesses form the detent holes or fastening holes. A plurality of recesses can favorably be made simultaneously by simple means in the flat sheet-metal panels.